Be sure to grind and clean area to be welded thouroughly. During the "stitching" process, be sure to chip/grind/clean out all the slag from the weld passes also. Try not to get too much heat in the arm at one time, could cause arm to bend or distort. Make a pass, chip, clean, then allow time to cool. After filling the joint in, grind smooth and add a "fish plate". This plate should cover the repair area, and be shaped into a diamond, with radiused points rather than 90 degree points, you will get more strength out of an arc than a point. Solid weld around this plate, using a skip pattern will also disperse heat and prevent distortion.